The Hall-Petch parameters of niobium determined by the grain size and extrapolation methods

Abstract

The Hall-Petch parameters are reported for niobium containing 580 wt. p.p.m. oxygen and 135 wt. p.p.m. nitrogen and are compared with those previously published. The results show that, contrary to iron, k y is lower than k f , and that the Hall-Petch plot is strongly affected by the substructure of the polycrystalline material. The Hall-Petch parameters are also determined by the extrapolation technique. The extrapolated lattice friction stress is grain-size independent and yields a better value than the Hall-Petch plot without the allowance for the effect of substructure. The grain-size dependence of the extrapolated k y parameter provides a method for the determination of the contribution of subgrain boundaries to the yield stress of niobium.